The pathogenesis of Herpesvirus infections in man and in experimental animals are investigated by characterization of viral isolates, and by examination of immunological response with particular emphasis on cell-mediated immunity. Patients with recurrent herpes simplex infections have elevated levels of serum antibody, and normal or elevated levels of lymphocyte cytotoxic against virus infected target cells. The efficacy and mechanism of action of antiviral compounds are examined in clinical trials, as well as in vitro. One such antiviral compound, adenine arabinoside (ara-A) appears to have efficacy in the treatment of herpes-zoster in the immunosuppressed, with little toxicity. Additional trials in Herpes Simplex infections in the immunosuppressed are underway, and trials in other Herpesvirus infections are planned for the next year. In vitro data indicates that ara-A may selectively inhibit viral directed DNA synthesis. le hemol